Dysregulated Autophagy Mediates Sarcopenic Obesity and Its Complications via AMPK and PGC1α Signaling Pathways: Potential Involvement of Gut Dysbiosis as a Pathological Link

New insights into the interplay between autophagy, gut microbiota and insulin resistance in metabolic syndrome

Metabolic syndrome (MetS) is a widespread and multifactorial disorder, and the study of its pathogenesis and treatment remains challenging. Autophagy, an intracellular degradation system that maintains cellular renewal and homeostasis, is essential for maintaining antimicrobial defense, preserving epithelial barrier integrity, promoting mucosal immune response, maintaining intestinal homeostasis, and regulating gut microbiota and microbial metabolites. Dysfunctional autophagy is implicated in the pathological mechanisms of MetS, involving insulin resistance (IR), chronic inflammation, oxidative stress, and endoplasmic reticulum (ER) stress, with IR being a predominant feature. The study of autophagy represents a valuable field of research with significant clinical implications for identifying autophagy-related signals, pathways, mechanisms, and treatment options for MetS. Given the multifactorial etiology and various potential risk factors, it is imperative to explore the interplay between autophagy and gut microbiota in MetS more thoroughly. This will facilitate the elucidation of new mechanisms underlying the crosstalk among autophagy, gut microbiota, and MetS, thereby providing new insights into the diagnosis and treatment of MetS.

High-fat diet induces sarcopenic obesity in natural aging rats through the gut-trimethylamine N-oxide-muscle axis

INTRODUCTION

The lack of suitable animal models for sarcopenic obesity (SO) limits in-depth research into the disease. Emerging studies have demonstrated that gut dysbiosis is involved in the development of SO. As the importance of microbial metabolites is starting to unveil, it is necessary to comprehend the specific metabolites associated with gut microbiota and SO.

OBJECTIVES

We aimed to investigate whether high-fat diet (HFD) causes SO in natural aging animal models and specific microbial metabolites that are involved in linking HFD and SO.

METHODS

Young rats received HFD or control diet for 80 weeks, and obesity-related metabolic disorders and sarcopenia were measured. 16S rRNA sequencing and non-targeted and targeted metabolomics methods were used to detect fecal gut microbiota and serum metabolites. Gut barrier function was evaluated by intestinal barrier integrity and intestinal permeability. Trimethylamine N-oxide (TMAO) treatment was further conducted for verification.

RESULTS

HFD resulted in body weight gain, dyslipidemia, impaired glucose tolerance, insulin resistance, and systemic inflammation in natural aging rats. HFD also caused decreases in muscle mass, strength, function, and fiber cross-sectional area and increase in muscle fatty infiltration in natural aging rats. 16S rRNA sequencing and nontargeted and targeted metabolomics analysis indicated that HFD contributed to gut dysbiosis, mainly characterized by increases in deleterious bacteria and TMAO. HFD destroyed intestinal barrier integrity and increased intestinal permeability, as evaluated by reducing levels of colonic mucin-2, tight junction proteins, goblet cells and elevating serum level of fluorescein isothiocyanate-dextran 4. Correlation analysis showed a positive association between TMAO and SO. In addition, TMAO treatment aggravated the development of SO in HFD-fed aged rats through regulating the ROS-AKT/mTOR signaling pathway.

CONCLUSION

HFD leads to SO in natural aging rats, partially through the gut-microbiota-TMAO-muscle axis.

Targeting gut microbiota in aging-related cardiovascular dysfunction: focus on the mechanisms

The global population is aging and age-related cardiovascular disease is increasing. Even after controlling for cardiovascular risk factors, readmission and mortality rates remain high. In recent years, more and more in-depth studies have found that the composition of the gut microbiota and its metabolites, such as trimethylamine N-oxide (TMAO), bile acids (BAs), and short-chain fatty acids (SCFAs), affect the occurrence and development of age-related cardiovascular diseases through a variety of molecular pathways, providing a new target for therapy. In this review, we discuss the relationship between the gut microbiota and age-related cardiovascular diseases, and propose that the gut microbiota could be a new therapeutic target for preventing and treating cardiovascular diseases.

Crosstalk between autophagy and insulin resistance: evidence from different tissues

Insulin is a critical hormone that promotes energy storage in various tissues, as well as anabolic functions. Insulin resistance significantly reduces these responses, resulting in pathological conditions, such as obesity and type 2 diabetes mellitus (T2DM). The management of insulin resistance requires better knowledge of its pathophysiological mechanisms to prevent secondary complications, such as cardiovascular diseases (CVDs). Recent evidence regarding the etiological mechanisms behind insulin resistance emphasizes the role of energy imbalance and neurohormonal dysregulation, both of which are closely regulated by autophagy. Autophagy is a conserved process that maintains homeostasis in cells. Accordingly, autophagy abnormalities have been linked to a variety of metabolic disorders, including insulin resistance, T2DM, obesity, and CVDs. Thus, there may be a link between autophagy and insulin resistance. Therefore, the interaction between autophagy and insulin function will be examined in this review, particularly in insulin-responsive tissues, such as adipose tissue, liver, and skeletal muscle.

Understanding the development of sarcopenic obesity

INTRODUCTION

Sarcopenic obesity (SarcO) is defined as the confluence of reduced muscle mass and function and excess body fat. The scientific community is increasingly recognizing this syndrome, which affects a subgroup of persons across their lifespans and places them at synergistically higher risk of significant medical comorbidity and disability than either sarcopenia or obesity alone. Joint efforts in clinical and research settings are imperative to better understand this syndrome and drive the development of urgently needed future interventions.

AREAS COVERED

Herein, we describe the ongoing challenges in defining sarcopenic obesity and the current state of the science regarding its epidemiology and relationship with adverse events. The field has demonstrated an emergence of data over the past decade which we will summarize in this article. While the etiology of sarcopenic obesity is complex, we present data on the underlying pathophysiological mechanisms that are hypothesized to promote its development, including age-related changes in body composition, hormonal changes, chronic inflammation, and genetic predisposition.

EXPERT OPINION

We describe emerging areas of future research that will likely be needed to advance this nascent field, including changes in clinical infrastructure, an enhanced understanding of the lifecourse, and potential treatments.

Mechanisms of Qingyi Decoction in Severe Acute Pancreatitis-Associated Acute Lung Injury via Gut Microbiota: Targeting the Short-Chain Fatty Acids-Mediated AMPK/NF-κB/NLRP3 Pathway

The pivotal roles of gut microbiota in severe acute pancreatitis-associated acute lung injury (SAP-ALI) are increasingly revealed, and recent discoveries in the gut-lung axis have provided potential approaches for treating SAP-ALI. Qingyi decoction (QYD), a traditional Chinese medicine (TCM), is commonly used in clinical to treat SAP-ALI. However, the underlying mechanisms remain to be fully elucidated. Herein, by using a caerulein plus lipopolysaccharide (LPS)-induced SAP-ALI mice model and antibiotics (Abx) cocktail-induced pseudogermfree mice model, we tried to uncover the roles of the gut microbiota by administration of QYD and explored its possible mechanisms. Immunohistochemical results showed that the severity of SAP-ALI and intestinal barrier functions could be affected by the relative depletion of intestinal bacteria. The composition of gut microbiota was partially recovered after QYD treatment with decreased Firmicutes/Bacteroidetes ratio and increased relative abundance in short-chain fatty acids (SCFAs)-producing bacteria. Correspondingly increased levels of SCFAs (especially propionate and butyrate) in feces, gut, serum, and lungs were observed, generally consistent with changes in microbes. Western-blot analysis and RT-qPCR results indicated that the AMPK/NF-κB/NLRP3 signaling pathway was activated after oral administration of QYD, which was found to be possibly related to the regulatory effects on SCFAs in the intestine and lungs. In conclusion, our study provides new insights into treating SAP-ALI through modulating the gut microbiota and has prospective practical value for clinical use in the future. IMPORTANCE Gut microbiota affects the severity of SAP-ALI and intestinal barrier function. During SAP, a significant increase in the relative abundance of gut pathogens (Escherichia, Enterococcus, Enterobacter, Peptostreptococcus, Helicobacter) was observed. At the same time, QYD treatment decreased pathogenic bacteria and increased the relative abundance of SCFAs-producing bacteria (Bacteroides, Roseburia, Parabacteroides, Prevotella, Akkermansia). In addition, The AMPK/NF-κB/NLRP3 pathway mediated by SCFAs along the gut-lung axis may play an essential role in preventing the pathogenesis of SAP-ALI, which allows for reduced systemic inflammation and restoration of the intestinal barrier.

Dietary Polysaccharides Exert Anti-Fatigue Functions via the Gut-Muscle Axis: Advances and Prospectives

Due to today's fast-paced lifestyle, most people are in a state of sub-health and face "unexplained fatigue", which can seriously affect their health, work efficiency, and quality of life. Fatigue is also a common symptom of several serious diseases such as Parkinson's, Alzheimer's, cancer, etc. However, the contributing mechanisms are not clear, and there are currently no official recommendations for the treatment of fatigue. Some dietary polysaccharides are often used as health care supplements; these have been reported to have specific anti-fatigue effects, with minor side effects and rich pharmacological activities. Dietary polysaccharides can be activated during food processing or during gastrointestinal transit, exerting unique effects. This review aims to comprehensively summarize and evaluate the latest advances in the biological processes of exercise-induced fatigue, to understand dietary polysaccharides and their possible molecular mechanisms in alleviating exercise-induced fatigue, and to systematically elaborate the roles of gut microbiota and the gut-muscle axis in this process. From the perspective of the gut-muscle axis, investigating the relationship between polysaccharides and fatigue will enhance our understanding of fatigue and may lead to a significant breakthrough regarding the molecular mechanism of fatigue. This paper will provide new perspectives for further research into the use of polysaccharides in food science and food nutrition, which could help develop potential anti-fatigue agents and open up novel therapies for sub-health conditions.

Therapeutic potential of alkaloid extract from Codonopsis Radix in alleviating hepatic lipid accumulation: insights into mitochondrial energy metabolism and endoplasmic reticulum stress regulation in NAFLD mice

Alkaloids are a class of naturally occurring bioactive compounds that are widely distributed in various food sources and Traditional Chinese Medicine. This study aimed to investigate the therapeutic effects and underlying mechanisms of alkaloid extract from Codonopsis Radix (ACR) in ameliorating hepatic lipid accumulation in a mouse model of non-alcoholic fatty liver disease (NAFLD) induced by a high-fat diet (HFD). The results revealed that ACR treatment effectively mitigated the abnormal weight gain and hepatic injury associated with HFD. Furthermore, ACR ameliorated the dysregulated lipid metabolism in NAFLD mice, as evidenced by reductions in serum triglyceride, total cholesterol, and low-density lipoprotein levels, accompanied by a concomitant increase in the high-density lipoprotein level. ACR treatment also demonstrated a profound anti-oxidative effect, effectively alleviating HFD-induced oxidative stress and promoting ATP production. These effects were achieved through the up-regulation of the activities of mitochondrial electron transfer chain complexes I, II, IV, and V, in addition to the activation of the AMPK/PGC-1α pathway, suggesting that ACR exhibits therapeutic potential in alleviating the HFD-induced dysregulation of mitochondrial energy metabolism. Moreover, ACR administration mitigated HFD-induced endoplasmic reticulum (ER) stress and suppressed the overexpression of ubiquitin-specific protease 14 (USP14) in NAFLD mice. In summary, the present study provides compelling evidence supporting the hepatoprotective role of ACR in alleviating lipid deposition in NAFLD by improving energy metabolism and reducing oxidative stress and ER stress. These findings warrant further investigation and merit the development of ACR as a potential therapeutic agent for NAFLD.

Gut microbiome plays a vital role in post-stroke injury repair by mediating neuroinflammation

Cerebral stroke is a common neurological disease and often causes severe neurological deficits. With high morbidity, mortality, and disability rates, stroke threatens patients' life quality and brings a heavy economic burden on society. Ischemic cerebral lesions incur pathological changes as well as spontaneous nerve repair following stroke. Strategies such as drug therapy, physical therapy, and surgical treatment, can ameliorate blood and oxygen supply in the brain, hamper the inflammatory responses and maintain the structural and functional integrity of the brain. The gut microbiome, referred to as the "second genome" of the human body, participates in the regulation of multiple physiological functions including metabolism, digestion, inflammation, and immunity. The gut microbiome is not only inextricably associated with dangerous factors pertaining to stroke, including high blood pressure, diabetes, obesity, and atherosclerosis, but also influences stroke occurrence and prognosis. AMPK functions as a hub of metabolic control and is responsible for the regulation of metabolic events under physiological and pathological conditions. The AMPK mediators have been found to exert dual roles in regulating gut microbiota and neuroinflammation/neuronal apoptosis in stroke. In this study, we reviewed the role of the gut microbiome in cerebral stroke and the underlying mechanism of the AMPK signaling pathway in stroke. AMPK mediators in nerve repair and the regulation of intestinal microbial balance were also summarized.

PGC-1α in osteoarthritic chondrocytes: From mechanism to target of action

Osteoarthritis (OA) is one of the most common degenerative joint diseases, often involving the entire joint. The degeneration of articular cartilage is an important feature of OA, and there is growing evidence that the mitochondrial biogenesis master regulator peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) exert a chondroprotective effect. PGC-1α delays the development and progression of OA by affecting mitochondrial biogenesis, oxidative stress, mitophagy and mitochondrial DNA (mtDNA) replication in chondrocytes. In addition, PGC-1α can regulate the metabolic abnormalities of OA chondrocytes and inhibit chondrocyte apoptosis. In this paper, we review the regulatory mechanisms of PGC-1α and its effects on OA chondrocytes, and introduce potential drugs and novel nanohybrid for the treatment of OA which act by affecting the activity of PGC-1α. This information will help to further elucidate the pathogenesis of OA and provide new ideas for the development of therapeutic strategies for OA.

Implication of Obesity and Gut Microbiome Dysbiosis in the Etiology of Colorectal Cancer

The complexity and variety of gut microbiomes within and among individuals have been extensively studied in recent years in connection to human health and diseases. Our growing understanding of the bidirectional communication between metabolic diseases and the gut microbiome has also highlighted the significance of gut microbiome dysbiosis in the genesis and development of obesity-related cancers. Therefore, it is crucial to comprehend the possible role of the gut microbiota in the crosstalk between obesity and colorectal cancer (CRC). Through the induction of gut microbial dysbiosis, gut epithelial barrier impairment, metabolomic dysregulation, chronic inflammation, or dysregulation in energy harvesting, obesity may promote the development of colorectal tumors. It is well known that strategies for cancer prevention and treatment are most effective when combined with a healthy diet, physical activity, and active lifestyle choices. Recent studies also suggest that an improved understanding of the complex linkages between the gut microbiome and various cancers as well as metabolic diseases can potentially improve cancer treatments and overall outcomes. In this context, we herein review and summarize the clinical and experimental evidence supporting the functional role of the gut microbiome in the pathogenesis and progression of CRC concerning obesity and its metabolic correlates, which may pave the way for the development of novel prognostic tools for CRC prevention. Therapeutic approaches for restoring the microbiome homeostasis in conjunction with cancer treatments are also discussed herein.

A Minireview Exploring the Interplay of the Muscle-Gut-Brain (MGB) Axis to Improve Knowledge on Mental Disorders: Implications for Clinical Neuroscience Research and Therapeutics

What benefit might emerge from connecting clinical neuroscience with microbiology and exercise science? What about the influence of the muscle-gut-brain (MGB) axis on mental health? The gut microbiota colonizes the intestinal tract and plays a pivotal role in digestion, production of vitamins and immune system development, but it is also able to exert a particular effect on psychological well-being and appears to play a critical role in regulating several muscle metabolic pathways. Endogenous and exogenous factors may cause dysbiosis, with relevant consequences on the composition and function of the gut microbiota that may also modulate muscle responses to exercise. The capacity of specific psychobiotics in ameliorating mental health as complementary strategies has been recently suggested as a novel treatment for some neuropsychiatric diseases. Moreover, physical exercise can modify qualitative and quantitative composition of the gut microbiota and alleviate certain psychopathological symptoms. In this minireview, we documented evidence about the impact of the MGB axis on mental health, which currently appears to be a possible target in the context of a multidimensional intervention mainly including pharmacological and psychotherapeutic treatments, especially for depressive mood.

Mechanisms Involved in Gut Microbiota Regulation of Skeletal Muscle

Skeletal muscle is one of the largest organs in the body and is essential for maintaining quality of life. Loss of skeletal muscle mass and function can lead to a range of adverse consequences. The gut microbiota can interact with skeletal muscle by regulating a variety of processes that affect host physiology, including inflammatory immunity, protein anabolism, energy, lipids, neuromuscular connectivity, oxidative stress, mitochondrial function, and endocrine and insulin resistance. It is proposed that the gut microbiota plays a role in the direction of skeletal muscle mass and work. Even though the notion of the gut microbiota-muscle axis (gut-muscle axis) has been postulated, its causal link is still unknown. The impact of the gut microbiota on skeletal muscle function and quality is described in detail in this review.

Gut Microbiota: A Key Regulator in the Effects of Environmental Hazards on Modulates Insulin Resistance

Insulin resistance is a hallmark of Alzheimer’s disease (AD), type II diabetes (T2D), and Parkinson’s disease (PD). Emerging evidence indicates that these disorders are typically characterized by alterations in the gut microbiota composition, diversity, and their metabolites. Currently, it is understood that environmental hazards including ionizing radiation, toxic heavy metals, pesticides, particle matter, and polycyclic aromatic hydrocarbons are capable of interacting with gut microbiota and have a non-beneficial health effect. Based on the current study, we propose the hypothesis of “gut microenvironment baseline drift”. According to this “baseline drift” theory, gut microbiota is a temporarily combined cluster of species sharing the same environmental stresses for a short period, which would change quickly under the influence of different environmental factors. This indicates that the microbial species in the gut do not have a long-term relationship; any split, division, or recombination may occur in different environments. Nonetheless, the “baseline drift” theory considers the critical role of the response of the whole gut microbiome. Undoubtedly, this hypothesis implies that the gut microbiota response is not merely a “cross junction” switch; in contrast, the human health or disease is a result of a rich palette of gut-microbiota-driven multiple-pathway responses. In summary, environmental factors, including hazardous and normal factors, are critical to the biological impact of the gut microbiota responses and the dual effect of the gut microbiota on the regulation of biological functions. Novel appreciation of the role of gut microbiota and environmental hazards in the insulin resistance would shed new light on insulin resistance and also promote the development of new research direction and new overcoming strategies for patients.

Dietary curcumin restores insulin homeostasis in diet-induced obese aged mice

Although aging is a physiological process to which all organisms are subject, the presence of obesity and type 2 diabetes accelerates biological aging. Recent studies have demonstrated the causal relationships between dietary interventions suppressing obesity and type 2 diabetes and delaying the onset of age-related endocrine changes. Curcumin, a natural antioxidant, has putative therapeutic properties such as improving insulin sensitivity in obese mice. However, how curcumin contributes to maintaining insulin homeostasis in aged organisms largely remains unclear. Thus, the objective of this study is to examine the pleiotropic effect of dietary curcumin on insulin homeostasis in a diet-induced obese (DIO) aged mouse model. Aged (18-20 months old) male mice given a high-fat high-sugar diet supplemented with 0.4% (w/w) curcumin (equivalent to 2 g/day for a 60 kg adult) displayed a different metabolic phenotype compared to mice given a high-fat high-sugar diet alone. Furthermore, curcumin supplementation altered hepatic gene expression profiling, especially insulin signaling and senescence pathways. We then mechanistically investigated how curcumin functions to fine-tune insulin sensitivity. We found that curcumin supplementation increased hepatic insulin-degrading enzyme (IDE) expression levels and preserved islet integrity, both outcomes that are beneficial to preserving good health with age. Our findings suggest that the multifaceted therapeutic potential of curcumin can be used as a protective agent for age-induced metabolic diseases.

The Interactome in the Evolution From Frailty to Sarcopenic Dependence

Biomarkers are essential tools for accurate diagnosis and effective prevention, but their validation is a pending challenge that limits their usefulness, even more so with constructs as complex as frailty. Sarcopenia shares multiple mechanisms with frailty which makes it a strong candidate to provide robust frailty biomarkers. Based on this premise, we studied the temporal evolution of cellular interactome in frailty, from independent patients to dependent ones. Overweight is a recognized cause of frailty in aging, so we studied the altered mechanisms in overweight independent elderly and evaluated their aggravation in dependent elderly. This evidence of the evolution of previously altered mechanisms would significantly support their role as real biomarkers of frailty. The results showed a preponderant role of autophagy in interactome control at both different functional points, modulating other essential mechanisms in the cell, such as mitochondrial capacity or oxidative stress. Thus, the overweight provoked in the muscle of the elderly an overload of autophagy that kept cell survival in apparently healthy individuals. This excessive and permanent autophagic effort did not seem to be able to be maintained over time. Indeed, in dependent elderly, the muscle showed a total autophagic inactivity, with devastating effects on the survival of the cell, which showed clear signs of apoptosis, and reduced functional capacity. The frail elderly are in a situation of weakness that is a precursor of dependence that can still be prevented if detection is early. Hence biomarkers are essential in this context.

A Narrative Review of Gut-Muscle Axis and Sarcopenia: The Potential Role of Gut Microbiota

Sarcopenia is a multifactorial disease related to aging, chronic inflammation, insufficient nutrition, and physical inactivity. Previous studies have suggested that there is a relationship between sarcopenia and gut microbiota,namely, the gut-muscle axis. The present review highlights that the gut microbiota can affect muscle mass and muscle function from inflammation and immunity,substance and energy metabolism, endocrine and insulin sensitivity, etc., directly or indirectly establishing a connection with sarcopenia, thereby realizing the “gut-muscle axis”.